A deep dive into ARC the Kubernetes operator to scale self-hosted runners

Stop manually managing runners. Get an on-demand, scalable GitHub Actions experience inside your own Kubernetes cluster with ARC.

#1about 2 minutes

Introducing the Actions Runner Controller for GitHub Actions

Actions Runner Controller (ARC) is an open-source project, now maintained by GitHub, for managing and scaling self-hosted runners on demand.

#2about 2 minutes

A live demonstration of auto-scaling self-hosted runners

See how a queued GitHub Actions workflow automatically triggers the creation of new runner pods in a Kubernetes cluster.

#3about 3 minutes

Understanding the core concept of Kubernetes control loops

Kubernetes operators use control loops, also known as reconciliation loops, to continuously check and enforce a desired state for resources.

#4about 1 minute

The high-level architecture of ARC and GitHub Actions

The controller runs in your Kubernetes cluster and communicates with GitHub to manage runner scale sets based on workflow demands.

#5about 1 minute

Why you should run ARC in a dedicated Kubernetes cluster

Isolate ARC from production workloads to prevent noisy neighbor problems and security risks from running arbitrary code.

#6about 4 minutes

How ARC controllers and custom resources work together

ARC installs a controller manager with multiple control loops, each responsible for reconciling a specific custom resource like runner scale sets.

#7about 5 minutes

The role of runner scale sets and the listener pod

Runner scale sets are pools of homogeneous runners, and a dedicated listener pod makes scaling decisions based on messages from GitHub.

#8about 6 minutes

A step-by-step workflow for scaling up a new runner

A workflow trigger sends a message to the listener, which patches a resource to increase the runner count, prompting a controller to create a new runner pod.

#9about 5 minutes

Exploring the open-source ARC repository on GitHub

A tour of the Actions Runner Controller codebase highlights its structure and the distinction between legacy community modes and the new GitHub-supported mode.

#10about 5 minutes

Defining custom resources for the ARC controller

The controller uses custom resource definitions (CRDs) to extend the Kubernetes API, creating new resource types like AutoscalingRunnerSet.

#11about 5 minutes

A look inside the controller's reconciliation function

The core logic of the operator resides in the reconciliation function, which compares the current state to the desired state and applies necessary changes.

#12about 3 minutes